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OBJECTIVE To develop a method to maintain the initial phenotype of airway smooth muscle (ASM) cells isolated from equine endobronchial biopsy specimens in long-term cell culture. SAMPLE Endobronchial tissue specimens (8 to 10/horse) collected from the lungs of previously healthy horses at necropsy (n = 12) and endobronchial biopsy specimens collected from standing, sedated, heaves-affected horses in clinical remission of the disease (5) and control horses (4). PROCEDURES A sampling protocol was developed to recover and maintain a contractile phenotype in ASM cells from endobronchial specimens from freshly harvested equine lungs and from healthy and heaves-affected horses. Immunologic techniques were used to evaluate the contractile phenotype of ASM cells in culture. RESULTS Characteristic ASM cells were successfully cultured from endobronchial tissue or biopsy specimens from both healthy and heaves-affected horses, and their contractile phenotype was maintained for up to 7 passages. Moreover, the capacity of cells at the seventh passage to contract in a collagen gel in response to methacholine was maintained. CONCLUSIONS AND CLINICAL RELEVANCE ASM cells isolated from equine endobronchial tissue and biopsy specimens were able to maintain a contractile phenotype in long-term cell cultures, suggesting they could be used for tissue engineering and in vitro studies of equine ASM cells.